(i) Technical Field
The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a semiconductor device having a semiconductor layer that includes gallium (Ga) and is formed on a silicon (Si) substrate by a vapor deposition method.
(ii) Related Art
A semiconductor device using a nitride semiconductor layer including Ga (gallium) as a composition element (GaN-based semiconductor layer) has attracted attention as devices capable of operating at high frequencies. An example of such a semiconductor device is a HEMT (High Electron Mobility Transistor). This type of semiconductor device frequently employs a silicon carbide (SiC) substrate or a sapphire substrate. Since these substrates are expensive, it is desired to develop a method for forming a semiconductor device having a GaN-based semiconductor layer on the silicon substrate. An MBE (Molecular Beam Epitaxy) method grows layers under high vacuum and has a difficulty in handling a source material of nitrogen. In contrast, an MOCVD (Metal Organic Chemical Vapor Deposition) method grows layers under reduced pressure or ordinary pressure, and handles NH3 and NH2 as a source material of nitrogen easily. Thus, the MOCVD method is widely used to grow GaN-based semiconductors. Japanese Laid-Open Patent Publication No. 2004-524250 discloses a method that includes the steps of providing a buffer layer made of AlN (aluminum nitride) on a silicon substrate and providing a semiconductor layer (channel layer) on the buffer layer by the MOCVD method.